The present invention relates to an ionic conductor, and more particularly to an ionic conductor remarkably improved in ionic conductivity through incorporation of a particular solid superacid as a dispersoid in Na.sub.1+x Zr.sub.2 P.sub.3-x Si.sub.x O.sub.12 (wherein 0.ltoreq.x.ltoreq.3) (hereinafter referred to as "NASICON") known as an oxide Na.sup.+ ionic conductor.
The ionic conductor is utilized as a solid electrolyte for cells, sensors, ECD (electrochromic display), etc.
Some brief description will now be given on an improvement in the ionic conductivity through addition of a dispersoid to an ionic conductor.
Ionic conduction occurs as the result of movement of ions in a solid. Therefore, the ionic conductivity is a value depending upon the number of movable ions, the mobility of ions, etc.
When a dispersoid is added to a solid ionic conductor, it attracts certain particular ions from the surface of the solid to form a layer having an apparently changed number of ions.
This layer exhibits higher ionic conductivity in terms of the number of movable ions, mobility, etc. than the solid ionic conductor as the base material, which contributes to an improvement in the ionic conductivity of the solid ionic conductor as a whole.
Various attempts have been made in the art on an improvement in the ionic conductivity through addition of a dispersoid to an ionic conductor. Examples of the attempt include addition of Al.sub.2 O.sub.3 to LiI [see C.C. Liang, J. Electrochem. Soc., 120, 1289 (1973)]. Further, there is a report on the addition of Al.sub.2 O.sub.3 to CuCl, HgI.sub.2, or the like.
Thus, the improvement in the ionic conductivity of an ionic conductor through addition of a dispersoid has hitherto been limited to the one attained by adding Al.sub.2 O.sub.3 to an ionic conductor comprising a metal halide.
In this case, it is presumed that conductive ions are attracted to the surface of Al.sub.2 O.sub.3 by virtue of the dielectric constant of Al.sub.2 O.sub.3, thereby forming a space charge layer having high ionic conductivity, which contributes to an improvement in the ionic conductivity of the ionic conductor (a so-called dielectric effect of Al.sub.2 O.sub.3).